The field of invention pertains to image displays that can selectively transmit or reflect actinic light.
Currently, images can be displayed on sheets of paper carrying permanent inks or displayed on electronically modulated surfaces such as cathode ray displays or liquid crystal displays. Sheet materials can carry magnetically written areas carrying ticketing or financial information, however magnetically written data is not visible.
A structure is disclosed in PCT/WO 97/04398, entitled xe2x80x9cElectronic Book With Multiple Display Pagesxe2x80x9d which is a thorough recitation of the art of thin, electronically written display technologies. Disclosed is the assembling of multiple electronically written display sheets into a xe2x80x9cbookxe2x80x9d, each sheet provided with means to individually address each page. The patent recites prior art in forming thin, electronically written pages, including flexible sheets, image modulating material formed from a bi-stable liquid crystal system, and thin metallic conductor lines on each page. The device described requires xe2x80x9c. . . transparent conducting polymers . . .xe2x80x9d formed over the light modulating material. Formation of transparent conductors of the required conductivity require complex vacuum sputtering and photo-lithographic processes.
Fabrication of flexible, electronically written display sheets is disclosed in U.S. Pat. No. 4,435,047. A first sheet has transparent ITO conductive areas and a second sheet has electrically conductive inks printed on display areas. The sheets can be glass, but in practice have been formed of Mylar polyester. A dispersion of liquid crystal material in a binder is coated on the first sheet, and the second sheet is pressed onto the liquid crystal material. Electrical potential applied to opposing conductive areas operates on the liquid crystal material to expose display areas. The display ceases to present an image when de-energized. The Taliq Company supplied products formed using the two sheet method. Offsetting the two sheets permitted connection to conductive traces on the two sheets.
The prior art typically requires multiple, separate layers to build up the display. The electrical traces and transparent conductive layers are typically formed through repeated vacuum deposition and photolithography of materials on the substrate. These processes are expensive and require long processing times on capital intensive equipment.
The prior art discloses isolating each conductor on separate sides of the display, and connecting the traces to drive electronics using solder connections, wire bonds or pressure contact. Such connections do require that both sets of traces be exposed on a surface for the connection process. The uniform, multi-layer structure prevents connection to the inner conductive layer.
Accordingly, it is an object of the present invention to provide a display which has opaque conductive images formed in an effective manner with a minimum number of steps.
This object can be achieved by a method of forming a display in which images can be selectively presented to a viewer, comprising the steps of:
(a) providing a transparent substrate;
(b) forming a transparent, electrically conductive coating over the transparent substrate;
(c) forming a light modulating layer including liquid crystal material in a polymer binder over the transparent, electrically conductive layer;
(d) forming by directly depositing opaque conductive material in an image wise pattern over the light modulating layer in the form of viewable and conductive images, the light modulating layer being effective in a first condition to prevent the viewing of the viewable and conductive images and in a second condition to permit the viewing of the viewable and conductive images; and
(e) providing electrical connections so that an electrical field can be applied across selected ones of such viewable and conductive images and the transparent, electrically conductive layer to cause the light modulating layer underlying the selected ones of the viewable and conductive images to change from the first condition to the second condition so as to present such viewable and conductive images for viewing to the viewer.
The disclosed structure has the advantage of directly forming opaque electrically conductive material in an image wise pattern thereby reducing the number of process steps that are required for transparent conductive images. The opaque, electrically conductive material can be a conductive ink deposited using screen printing. Printing processes are widely available, and simple and effective means to provide custom display. Displays in accordance with the present invention can be in the form of display sheets that can be made using conventional coating technology. A single large area of sheet material can be coated and formed into different types of displays by printing opaque, electrically conductive indicia onto the coated sheet.